Sweatcoin, a London-based health and fitness start-up which rewards users for being active by paying them in its own digital currency, has raised $5.7m (£4m) to expand to Europe and Asia.

The free app tracks a user's movement and currently rewards every 1,000 steps recorded with 0.95 'sweatcoins', which people can then spend on a variety of things from fitness gear and workout classes to experiences, food and clothes.

The company's digital currency is currently accepted by about 300 vendor partners in the US and UK, including Boohoo.com, Graze and Hellofresh.

The Sweatcoin app, which is currently only available in the UK, Ireland and the US, has five million registered users.

"We are thrilled to have backing from such a great group of investors," said co-founder Anton Derlyatka.

"More than 5m registered users in less than 12 months and more than 2m weekly actives is a good start. We will now continue focusing on great user experience and global expansion."

Co-founder Oleg Fomenko added: "This round will allow us to build out the product and technology team to improve our step-verification algorithm and develop an open-source blockchain DLT technology to allow Sweatcoin to be traded like any other major crypto- or fiat currency."

Sweatcoin was initially released in a public beta in the UK and US App Stores in May and August 2016 respectively with a full iOS version available since late December 2016, and an Android version available since April 2017.

It has been the most downloaded app in the health and fitness category since September 2017.